You can use the CD the way it is as a signal mirror, or you can reshape it for your purposes. I am in favor of reshaping it because the product is consequently smaller and allows you to save space. This also helps to stow the mirror in one of the many Altoids can survival kits featured here on Instructables.
You can follow this Instructable, or watch the video explaining how to do the project.
Step 1: Materials
-A CD (that you do not mind breaking)
What you will use:
Step 2: Video
* I wasn't able to embed the video in the Instructable for some reason. I will try to correct it.
Step 3: Shape the Mirror
Remember: if you want the mirror to fit in the tin, mark it slightly smaller than the tin itself.
Step 4: Cut the CD
Step 5: Tape Time!
Step 6: How to Signal
Enjoy your new survival tool!